Light source

ABSTRACT

A light source comprises a matrix of micro-filaments able to emit light by incandescence when powered by an electrical current. According to the invention, on the matrix electrical and/or mechanical connections are obtained by means of agglomerations of carbon nanotubes at least partially ordered with respect to each other.

This is a divisional of application Ser. No. 10/392,813, filed Mar. 21,2003, which claims priority to TO2002A000256 filed Mar. 22, 2002, thedisclosures of both of which are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing an incandescentlight source and a light source obtained according to such method.

The first working step followed for purposes of producing filaments forincandescent light sources typically consists of preparing a mixture oftungsten and metallic additives, which is subsequently sintered in theform of bars.

The bars thus obtained are then subjected to hammering and drawing withsuccessive passages, until obtaining a continuous wire with the desireddiameter; said wire is subsequently wound in a spiral and cut to therequired length to be ready, after a stabilising heat treatment, to bemounted onto a respective support to be inserted in the light source.

In the case of common incandescent lamps, the filament is maintained inposition thanks to respective end conductors and intermediate hooks; theconductors serve both as supports and to carry electrical power to thefilament, and for this reason they are connected to the base of thelamp; the hooks instead serve solely as supports. The electricalconnections between the filament and the conductors are mainly obtainedby soldering, for instance by means of capacitive discharge, or byfolding and upsetting the conductor on the filament. Since the hooks donot have to provide electrical contact, they are generally folded inloops, through which the filament passes.

Other types of light sources provide for the use of matrices offilaments able to emit light by incandescence when powered by anelectrical current, as well as the use of electronic control means forthe lighting of some or all filaments in the matrix.

The individual filaments can be obtained with multiple coupled filaments(two, three, or more), or with a single filament wound in a simple ormultiple spiral or, in the simplest case, they can consist of a segmentof individual filament. The aforesaid matrix consists of a quantity offilaments connected in various ways, for instance in series, inparallel, in series-parallel, in parallel-series, in a netconfiguration.

Regardless of the chosen configuration, the number of the filament in amatrix can be high, where the respective arrangement presupposes

connections between the power supply conductors and the filaments,and/or

connections between the filaments, and/or

connections of any conductors or hooks intermediate to the filaments.

One of the reasons limiting the wider use of light sources with filamentmatrices is currently constituted by the difficulty in obtaining theaforesaid connection in a simple, effective and economical manner.

Another difficulty to overcome is given by the fact that, especiallywhen the number of filaments in a matrix is high, there aremanufacturing problems linked to their positioning.

In general terms, the present invention is aimed at solving theaforesaid drawbacks.

SUMMARY OF THE INVENTION

Given that the dimensions and number of connections have considerableinfluence on the quantity of heat that is dissipated, and hence on theefficiency of the filament matrix, a first object of the presentinvention is to indicate a method that allows to obtain connectionshaving extremely reduced dimensions.

Given that the operating temperature of the connections of the filamentmatrices is very high (˜2500° C.), a second aim of the present inventionis to indicate a method that allows to obtain connections with anadequate ability to withstand such temperatures, without the productionof polluting gases as a result of the operating temperature of theconnections.

A third object of the invention is to indicate a method that, even inthe presence of highly complex filament matrices, allows to obtain theconnections in a simple manner, in order to contain production costs.

A fourth object of the invention is to indicate a method for obtainingfilament matrices having very low manufacturing defect rate, in order tolimit production waste.

The aforesaid objects are achieved, according to the present invention,by a method for producing an incandescent light source comprising acomplex or matrix of micro-filaments able to emit light by incandescencewhen they are powered by an electrical current, the method comprisingthe production on the micro-filament complex, of one or more electricaland/or mechanical connections, characterised in that the connection orconnections are obtained using an agglomeration of carbon nanotubes atleast partially ordered with respect to each other.

An additional object of the invention is to indicate a method thatallows to obtain in simple fashion the positioning of the filamentsduring the manufacturing phase.

Said additional object is achieved, according to a further aspect of theinvention, by a method in which the micro-filament matrix is formedextending a single uninterrupted wire constituted by a material selectedamong tungsten or tungsten-based metallic alloys along a complex pathdefined by a plurality of positioning elements arranged in remoteposition from each other, the path being such that segments of theuninterrupted wire that extend from different positioning elements aremutually crossed.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are contained in the accompanyingclaims, which form an integral part of the present description.

Further objects, characteristics and advantages of the present inventionshall become readily apparent from the following description withreference to the accompanying drawings, provided purely by way of nonlimiting example, in which:

FIG. 1 is a perspective view of a matrix of incandescence filaments of alight source obtained in accordance with the teachings of the presentinvention,

FIG. 2 is a perspective view of a detail of a part of the matrix of FIG.1, in enlarged scale,

FIG. 3 is a plan and partially cut-off view of a tool used to producethe matrix of FIG. 1,

FIG. 4 is a lateral section according to the line III-III of FIG. 3,

FIG. 5 is a perspective view of a portion of the tool of FIG. 3, duringits employment,

FIG. 6 is a lateral section of the tool of FIG. 3, during itsemployment.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the reference number globally designates a filament matrixproduced in accordance with the teaching of the present invention.

The matrix 1 comprises two lateral power supply conductors 2 made ofmetallic material and a plurality of micro-filaments 3, where the term“micro-filaments” means individual pieces of filament that emit lightwhen an appropriate electrical current flows through them, reaching atemperature of about 2800° K.

The various micro-filaments 3 are arranged according to a “net”configuration, and are then mechanically and electrically connected toeach other as well as to the conductors 2; the reference number 2Adesignates hooks for the positioning and support of the matrix 1, alsoconnected to some micro-filaments 3. For this purpose, also withreference to FIG. 2, the reference number 4 designates the connectionsbetween some micro-filaments 3.

The elementary filament of the matrix 1 can be in different forms:individual wire, multiple wires coupled in parallel, wire wound in aspiral.

In an advantageous embodiment, the filament system of the matrix 1 canbe obtained in the aforesaid forms using a single uninterrupted wire,which allows considerably to simplify the production process, whilstreducing the defect rate of the final product.

The materials used to obtain the aforesaid wire can be tungsten, arhenium-tungsten or other alloys with tungsten; the rhenium-tungstenalloy is particularly indicated because it improves the working live ofthe filament and its mechanical strength.

For the purposes of producing the matrix 1 by means of a single startingwire, an appropriate equipment is used, globally designated as 10 inFIGS. 3 and 4.

The equipment 10 has a main body 11, substantially T-shaped, having aplanar upper portion 12, centrally opened, wherefrom departs downwards alower portion 13 shaped as a conduit, which is coupled in sealed fashiononto a respective support S.

The central area of the upper portion 12 is provided for housing a pairof superposed planar elements, designated as 14A and 14B; for thispurpose, on opposite parts of the upper portion 12 are providedrespective pins 15, whereon are fitted the two planar elements 14A and14B, with an operative sequence that will be described below.

Inferiorly to the planar element 14A, in a respective seat defined incorrespondence with the central opening of the upper portion 12, asupport 16 is provided.

In the preferred embodiment of the invention, the support 16constitutes, together with the planar elements 14A and 14B, a mould usedfor purposes of obtaining the connections 4, as shall become readilyapparent below. To this end, within the two planar elements 14A and 14Bare defined arrays of through cavities CP, positioned between two largercavities CM, wherein the conductors 2 are destined to be positioned.

In the peripheral area of the upper portion 12, outside the positioningarea of the planar elements 14A and 14B are positioned in pairs fourgroups of pins 17A, 17B, 17C and 17D, used for positioning a singletungsten-based wire; to the pins 17C and 17D of two of said groups arealigned respective elastic tensioning elements 18, for instance in theform of springs, known in themselves.

As stated, for the purposes of producing the matrix 1 a singletungsten-based wire is used, designated as 19, whose two ends aredesignated 19A and 19B in FIG. 4.

For this purpose, on the portion 12 of the body 11 is positioned thesupport or filter 16 and thereon the planar element 14A.

The wire 19 is then unwound prevalently between the positioning pins17A, 17B and the tensioning elements 18, in such a way as to form thepattern visible in the figure.

The pattern is thus arranged substantially on a single plane and in sucha way that the crossings between the micro-filaments are incorrespondence with the cavities CP of the planar element 14A; in therespective cavities CM can instead be positioned the conductors 2; inthe cavities CM which are in correspondence with some of the crossingsat the lateral ends of the pattern of filaments can be positioned thehooks 2A.

To the equipment 10 is then also associated the planar element 14B, themicro-filament pattern thus being interposed between the two elements14A and 14B, with the crossings positioned in correspondence with thethrough cavities CP of the elements 14A and 14B, as noted in FIG. 5(note than in said figure, as in FIG. 6, the thickness of the element14A and 14B is increased for the sake of greater clarity ofrepresentation).

Into the cavities CP and CM is then poured the material used to obtainthe connections 4 of the matrix 1 of FIG. 1 and 2; at the end of saidoperation of moulding the connections 4, the matrix 1 now formed isfreed from the equipment 10 and by the excess segments of tungsten wire,and for the latter operation one can for instance use laser cutting.

As is readily apparent, use of the equipment 10 allows to obtain thematrix 1 of micro-filaments 3 starting from a continuous wire, withevident advantages in terms of simplicity and regularity of positioningof the filaments themselves.

According to an important aspect of the present invention, for purposesof obtaining the connections 4 carbon nanotubes are used: this is one ofthe most stable allotropic forms of carbon.

Carbon nanotubes can be depicted as a cylindrical structure constitutedby one or more graphite sheets wound about a central axis. At the ends,the walls of the tube are curved until they close in on themselvesforming a sort of “cap” with conical or semi-spherical shape, withmolecular geometry similar to those of fullerenes.

The diameter of carbon nanotubes ranges from 1 to 50 nm whilst theirlength can reach a few tens of microns; they have exceptionalmechanical, electrical and thermal properties: they are stronger andlighter than steel and they conduct electricity like metals do, withhigh ultimate tensile stress (˜100 Gpa), very high Young module (˜1.8Tpa), low density (˜1.3 g/cm³), high electrical conductivity (˜10e+06ohm−1.m−1), high thermal conductivity (˜2000 W·m−1·K−1).

For an agglomeration of carbon nanotubes to be provided with highmechanical strength, the nanotubes must be mutually aligned.

However, due to the high inter-tube cohesion forces due to electrostaticinteractions, carbon nanotubes are usually in aggregate but disorderlyform.

A possible way to solve this problem is to produce the carbon nanotubesalready mutually aligned, using chemical deposition techniques. Whilesuch processes are applicable, they are costly; in the preferredembodiment of the invention, therefore, it is proposed to start from thesame disorderly nanotube aggregates, in the form of powder.

The preparation of structured material from nanotubes requires saidaggregates to be initially destroyed, and then to allow the nanotubes toalign themselves partially or total.

To this end, in accordance with the method according to the invention, asurface-active solution is prepared, within which the carbon nanotubesare dispersed by agitation. The suspension thereby obtained ispreferably subjected to an ultrasound treatment, for a time intervalconsidered adequate to favour the disaggregation of the nanotubeagglomerates.

In this phase, the surface-active compound is adsorbed on the walls ofthe nanotubes, covering and forming a molecular layer around them whichfavours the disaggregation of the agglomerations by effect of thesuppression of the electrostatic attraction forces between nanotube andnanotube.

The suspension preparation step is carried out in manners that are clearto those versed in the art, taking into account the solution propertiesof carbon nanotubes and the ternary phase diagramnanotubes/water/surface-active compound.

An excess of surface-active compound would result in the formation ofagglomerations of surface-active compound molecules (micelles), therebyreducing the adsorption effect on the nanotube walls;surface-active/surface-active interactions would be privileged oversurface-active/nanotube interactions, thus leaving the nanotubeagglomerations unaltered. Conversely, small quantities of surface-activecompound do not cause the desired effect of coating individual nanotubemolecules.

Essentially, therefore, the nanotube suspension should be handled withcare, avoiding any dilution that would result in imbalances.

Once the time required to achieve the disaggregation of the nanotubeagglomerations has elapsed, an adequate quantity of suspension is placedin the mould formed by the planar elements 14A, 14B and by the support15, which here serves the function of porous filter, and to this end ismade for instance of Teflon or polycarbonate.

The shape of the aforesaid mould, or rather of the various cavities CP,determines the shape of the connections 4 and contains, as stated, theportions of micro-filaments 3, of the conductors 2 and of any hooks 2Athat are incorporated in the matrix 1.

In all the various cavities CP (and CM), which are as in FIG. 5, is thenplaced the suspension of the disaggregated nanotubes in thesurface-active compound, which is substantially in the form of a paste,designated as P in FIG. 6. As is readily apparent, an advantage of thetechnique proposed herein is that all connections 4 can be executed in asingle operation.

The suspension contained in the mould formed by the planar elements 14A,14B and by the filter 15 is then filtered.

This is preferably accomplished by creating a vacuum below the filter15, i.e. in the lower conduit-like portion 13 of the body of theequipment 10, visible in FIG. 4, for instance by aspiration from afitting R of the support S.

Filtering is then followed by a series of washings of the mould, firstwith water and then with methyl alcohol, to eliminate all traces ofsurface-active compound; the solid part left inside the cavity CP, CM ofthe mould is then dried, thereby obtaining a compact and strong mass ofnanotubes, which achieves the connections 4.

In this regard it should be noted that the washing and drying steps arecharacterised by the directionality of the flow of the fluid used(liquid and air) as highlighted by the undulated vertical arrows in FIG.6. The nanotubes are crushed by the pressure of the fluid, in order togenerate inter-tube cohesion forces favouring their re-aggregation inorderly fashion, i.e. mutually aligned or parallel. It should be notedthat directionality of flow is important to obtain the mutual alignmentof the nanotubes, necessary condition to provide mechanical strength tothe agglomeration.

This purpose is served by the filtering element 15, which constitutes infact the lower wall of the mould, and by an adequate pressuredifferential to initiate the flow.

Should it be necessary, it is possible to operate with a non optimalsuspension, thereby also obtaining an only partial alignment of thenanotubes inside the connections 4. Although the partial alignment ofthe nanotubes confers reduced strength, said strength is nonethelesssufficient for the mechanical stresses typical of the connections of afilament matrix of the type examined herein. This considerationtherefore allows to choose a compromise that can simplify the productionsteps, also in terms of time.

From the above description, the characteristics of the present inventionare readily apparent, as are its advantages. Among them, it should bestressed that use of carbon nanotubes with the method according to theinvention allows:

to achieve connections 4 of extremely reduced dimensions, with evidentbenefits in terms of quantity of heat dissipated and matrix efficiency;

to obtain connections 4 able to withstand high operating temperatures,without the production of polluting gases;

to achieve the connections 4 simultaneously, in simple and rapid fashionand with low defect rate, with consequent reduction of the productioncosts.

Obtaining the matrix 1 starting from a single base wire, by means of theequipment based on opposite positioning pins and tensioning elements,allows to obtain in simple fashion the positioning of the filamentsduring production.

Naturally, without changing the principle of the invention, theconstruction details and the embodiments may vary from what is describedand illustrated purely by way of example herein.

The conductors 2 and any positioning hooks 2A, instead of beingconfigured as distinct components to be connected to the matrix, couldbe obtained directly from carbon nanotubes, in the course of theproduction of the connections 4; in this case, in the cavity CM of themould and in those that may be provided for the hooks, only thesuspension P would be present, then subjected to filtering, washing anddrying as described above, in order to obtain the conductors and thehooks directly.

The shape of the cavities CP could be different from those illustratedby way of example, as it may be variable according to constructiverequirements; the same holds true for the cavities CM and for theadditional cavities for any hooks for positioning the matrix.

The equipment 10 could be conceived in such a way as to allow moving orin any case adjusting the position of the pins 17 and of the tensioningelements 18, and to the upper portion 12 of the body 11 could beassociated planar elements 14B and 14B bearing arrays of cavities CP, CMwith different shapes, in order to obtain various patternconfigurations.

In accordance with possible variations in the implementation of themethod according to the invention, the alignment of the nanotubesnecessary to obtain the material used for the connections 4 can beobtained with other techniques, for instance based on the use ofelectrical fields or magnetic fields. In particular, manners of aligningthe nanotubes alternative to the one described in detail above can beall those described in WO-A-01 30694, whose teachings in this regard areto be considered incorporated herein by reference.

The single wire could be arranged to travel even several times over thesame path defined by the positioning pins 17A-17D and by the tensioningelements 18, in which case the micro-filaments 3 would be formed by askein-like bundle of filaments; the single wire could also have, alongits development, spiral segments alternating with rectilinear segments,or be entirely in the form of a continuous spiral.

The use of carbon nanotubes in the manner described and in the mannersmentioned herein can be advantageously applied also for purposes ofobtaining connections between mutually independent micro-filaments, i.e.not formed starting from a single uninterrupted base wire.

1. A light source comprising a complex of micro-filaments able to emitlight by incandescence when powered by an electrical current and one ormore electrical and/or mechanical connections formed by a respectiveagglomeration of carbon nanotubes at least partially ordered or alignedwith each other.
 2. The light source, as claimed in claim 1, wherein theconnection or connections comprise at least one of a connection betweentwo micro-filaments in the complex of micro-filaments, a connectionbetween a micro-filament in the complex of micro-filaments and aconductor for supplying power to the complex of micro-filaments, and aconnection between a micro-filament in the complex of micro-filamentsand a positioning element or support of the complex of micro-filaments.3. The light source, as claimed in claim 2, wherein at least one of saidconductor and said positioning or support element is entirely made froma respective agglomeration of carbon nanotubes.
 4. The light source asclaimed in claim 1, wherein the micro-filaments are constituted by amaterial of tungsten or a tungsten-based metallic alloy.
 5. The lightsource as claimed in claim 1, wherein the micro-filaments consist of askein-like bundle of filaments.
 6. The light source as claimed in claim1, wherein the micro-filaments are mutually connected according to aseries-parallel configuration.
 7. The light source as claimed in claim1, wherein the micro-filaments are mutually connected according to aparallel-series configuration.
 8. The light source as claimed in claim1, wherein the micro-filaments are mutually connected according to a netconfiguration.
 9. A light source comprising a complex ofmicro-filaments, able to emit light by incandescence when powered by anelectrical current, and one or more electrical and/or mechanicalconnections, the micro-filaments being formed by a first material andthe connections being formed by a second material, wherein theconnection or connections are formed by a respective agglomeration ofcarbon nanotubes.
 10. The light source as claimed in claim 9, whereinthe carbon nanotubes are at least partially ordered with each other. 11.The light source, as claimed in claim 10, wherein the connection orconnections comprise at least one of a connection between twomicro-filaments in the complex of micro-filaments, a connection betweena micro-filament in the complex of micro-filaments and a conductor forsupplying power to the complex of micro-filaments, and a connectionbetween a micro-filament in the complex of micro-filaments and apositioning element or support of the complex of micro-filaments. 12.The light source, as claimed in claim 11, wherein at least one of saidconductor and said positioning or support element is entirely made froma respective agglomeration of carbon nanotubes.
 13. The light source asclaimed in claim 9, wherein the micro-filaments are constituted by amaterial of tungsten or a tungsten-based metallic alloy.